(1) Field of the Invention
The present invention relates to a button telephone apparatus which contains an IP (Internet Protocol) trunk.
(2) Description of the Related Art
Recently, there has been provided a system which integrates a voice network with a data network. Such a system employs an IP trunk (including a VoIP [Voice over Internet Protocol] unit) which can convert a voice into IP packets so that voice information can be transmitted and received on an IP network such as the Internet (see JP-A-2002-262345).
In an IP trunk connected to a broadband line such as an optical line, ADSL (Asymmetric Digital Subscriber Line) or the like, a plurality of voice communication channels can be set on a single line. In such an IP trunk, the number of voice channels is generally fixed.
However, the IP trunk having a fixed number of voice channels experiences a reduction in a band (or rate) for making voice communications as the traffic of data communications increases, resulting in a problem of a degraded voice quality due to echoes and delays which can occur in the voice communications.
JP-A-2002-262345 describes that more voice communications are achieved by temporarily using data communication channels for voice calls, as required. However, in this method, the data communication channels may be used for voice calls even if the traffic of data communications increases. Since the number of data communication channels is reduced in this way irrespective of the traffic of data communications, this method can suffer from such troubles as an inability to communicate data and the long amount of time required for data communications in some cases.